1. Field of Invention
This invention pertains to reagents for use in the kinetic method for the determination of glucose with glucose dehydrogenase.
2. Description of the Prior Art
Kinetic methods for the determination of glucose concentrations in samples, e.g., body fluids, with glucose dehydrogenase are known. D. Banauch, W. Brummer, W. Ebeling, H. Metz, H. Rindfrey, H. Lang, K. Leybold and W. Rick, Z. Klin. Chem. Klin. Biochem., 13:101 (1975), reported a kinetic method for determining glucose using glucose dehydrogenase. The reagent of Banauch et al. comprised 160 mmoles/l of tris buffer, pH 7.8, 0.6 U/ml glucose dehydrogenase, and 2.1 mmole/l NAD. This reagent, when employed in the kinetic method was stated to have yielded a calibration curve linear up to 1,000 mg/dl (the sample to reagent ratio was not specified).
Lutz et al., Clinical Chemistry, 21 (10):1372 (1975), also disclosed a kinetic method for the determination of glucose using the glucose dehydrogenase reaction. The glucose dehydrogenase reagent employed by Lutz et al. comprised 86.5 mg of NAD and 6 mg of glucose dehydrogenase in 50 ml of tris buffer (pH 7.8). Lutz et al. reported a deviation from linearity of their uncorrected glucose dehydrogenase method as being 4% at 300 mg%, 8% at 500 mg% and 19% at 1000 mg% using a sample to reagent ratio of 1:41. Based upon their work, Lutz et al. concluded that "(i)t therefore seems impossible to reach the linearity claimed by others (Banauch et al., supra)."
Lutz, Clinical Chemistry, 22(6):929 (1976), disclosed an attempt to improve the linearity of the kinetic method for determination of glucose by adding competitive inhibitors for GDH to the enzymatic reagent in order to increase the linearity of the reaction. Using an equation to correct for nonlinearity, Lutz was only able to increase the range of linearity to about 500 mg/dl using a sample to reagent ratio of 1:41.
H. Rindfrey, R. Helger and H. Lang, Kinetic Glucose Determination with Glucose Dehydrogenase, Z. Anal. Chem., 279:196 (1976), subsequently confirmed Lutz et al.'s allegation that the Banauch et al. article's statement as to the range of linearity was erroneous. Rindfrey et al. disclosed that the kinetic glucose determination with glucose dehydrogenase was linear up to 300 mg/dl and that at 500 mg/dl the error was -10%. (The sample to reagent ratio employed was 1:50.)